Recently, a light-emitting diode (hereinafter, referred to as “LED”) has been increasingly used as a light source for a surface light source device (illumination apparatus) of an edge-lit type with a hollow structure without using a light guide plate. In such a surface light source device, there is a case where a combination of an LED and a light flux controlling member (lens) may be used in order to control the distribution of light emitted from an LED (see PTL 1, for example).
FIG. 1 is a sectional view illustrating the configuration of surface light source device 10 set forth in PTL 1. As illustrated in FIG. 1, surface light source device 10 has hollow unit case 11, LED light source units 12 disposed linearly on two side surfaces facing each other inside unit case 11, condenser lens 13 that controls the distribution of light emitted from LED light source unit 12, reflection member 14 disposed at the side of a bottom surface inside unit case 11, and light-emitting planar member 15 disposed at the side of a top surface inside unit case 11. Reflection member 14 has inclined surfaces that incline from a ridge line positioned at the center between the side surfaces facing each other of unit case 11 toward the side surfaces.
The distribution of light emitted from LED light source unit 12 is controlled by condenser lens 13. Light emitted from condenser lens 13 is diffused and reflected at reflection member 14, and then transmitted through light-emitting planar member 15 to be emitted toward the outside. In surface light source device 10 set forth in PTL 1, surface roughness Ra of reflection member 14 is set to be greater than 1 μm, thereby achieving equalization of the luminance distribution in the light emitting area.